Economical application of reaction resin molded materials to the manufacture of insulating components, requires quick-hardening reaction resins that shorten mold occupancy times and thus production costs. In the electrical industry, acid-anhydride-hardenable epoxy resins are predominantly used for the manufacture of mechanically-thermally and electrically high-quality reaction resin molded materials. Processes analogous to injection molding of resins adjusted for high reactivity are known wherein the mold occupancy times can be reduced considerably from conventional casting procedures. In such processes low viscosity epoxy resin compounds usually containing fillers are forced into casting molds. The casting molds, as a rule, have a temperature substantially higher than the resin compound which gells faster at the higher temperatures than in conventional procedures, wherein heat is applied, usually in steps, only after the casting, to effect gelling and cross-linking of the epoxy resins.
A disadvantage of using acid-anhydride-hardenable epoxy resins in processes analogous to injection molding is a decline in the mechanical properties of the resulting injection-molded bodies in comparison to conventional castings, e.g., reduced bending strength. The reduced mechanical properties are apparent from available technical literature and have been documented by our own investigations summarized in Table 1 below.
TABLE 1 __________________________________________________________________________ Molded Material Properties of Acid-Anhydride- Hardened Epoxy Resins as a Function of the Standard-Rod Fabrication Conditions Molded Material Properties.sup.(3) Epoxy Resin Composition Standard Rod BF SZ T.sub.M (Abbreviated Designation).sup.(1) Fabrication Conditions.sup.(2) N/mm.sup.2 Nmm/mm.sup.2 .degree.C. __________________________________________________________________________ BAGE 100 MT.sup.(4) KGT: 1 h 100.degree. C. 124 13 115 HHPSA 80 MT 3 h 130.degree. C., 16 h 180.degree. C. DMBA 0,5 MT NSG (3 bar): 10 min 150.degree. C. 116 11 117 QM I 360 MT 16 h 180.degree. C. HYEP 100 MT KGT: 1 h 100.degree. C. 133 12 127 MTHPSA 110 MT 3 h 130.degree. C., 16 h 180.degree. C. lMI 0,5 MT NSG (3 bar): 10 min 150.degree. C., 121 10 133 QM I 380 MT 16 h 180.degree. C. __________________________________________________________________________ .sup.(1) For chemical designation see Table 10 .sup.(2) KGT: Conventional casting technique NSG: Lowpressure fastcasting technique .sup.(3) BF = bending strength SZ = impact strength T.sub.M = dimensional heat resistance according to Martens .sup.(4) MT = mass parts
Another disadvantage of anhydride-cross-linkable epoxy resins is that modifications increasing the dimensional heat resistance of the molded materials to temperatures above 150.degree. C. usually cause losses in their mechanical properties. In contrast, the increasingly higher thermal stress requirements for reaction resin molded materials in the electrical industry calls for quick-hardening reaction resins from which molded materials with high dimensional heat stability and at the same time, good mechanical properties can be made.
Known highly heat-resistant reaction resin materials may be prepared by thermal hardening of reaction resin mixtures of polyepoxides and polyiscoyanates, so-called EP/IC resins, in the presence of hardening catalysts (see DE-AS No. 1 115 922: column 5, lines 9 to 14, and DE-AS No. 1,963,900: column 1, lines 4 to 13 and 48 to 60). For the preparation, EP/IC resins are described in the literature (U.S. Pat. No. 4,070,416) which have a formula mole ratio of the epoxy and isocyanate groups (EP:IC) of less than 1. It is pointed out there that the best thermal molded-material properties of the molded materials containing oxazolidinone and isocyanurate rings (OX/ICR molded materials) are obtained if EP/IC resins with a EP:IC mole ratio of 0.2 to 0.7 are cross-linked in the temperature range between 70.degree. and 130.degree. C. and are post-hardened at temperatures of up to 220.degree. C. The molded materials manufactured in this manner, exhibit excellent dimensional heat stability but have only moderate mechanical properties and insufficient temperature cycle resistance. The mechanical properties are known to deteriorate with increasing polyisocyanate content in the EP/IC resins.
It is therefore understandable that it has been suggested that the mechanical properties of OX/ICR molded materials may be improved by incorporating flexibilizing or elastifying components in the resins. Proposed suitable polyepoxide components for the EP/IC resins are pre-polymer oxazolidinones with terminal epoxy groups (U.S. Pat. No. 3,979,365). However, the viscosity of these polymers, is very high so that they are difficult to inject without using solvents. Another proposal is to add polyglycidyl esters of dimerized fatty acids to EP/IC resins with other polyepoxides (U.S. Pat. No. 4,100,118). While these polyglycidyl esters have a low viscosity, they exhibit a poor mixing behavior in the EP/IC resins. It has also been proposed to add copolymers of butadiene to the EP/IC resins for instance, copolymers with acrylonitrile as an elastifying component (U.S. Pat. Nos. 4,128,531 and 4,130,546). These copolymers have functional groups such as hydroxyl and carboxyl groups, and the carboxyl groups may be reacted with polyepoxides. These copolymers especially in the case of filler-containing EP/IC resins, cannot be used efficiently in injection molding processes, due to their high viscosity. In addition, such copolymers are difficult to process, since they exhibit a high tendency to separate from the EP/IC resin. It is a further disadvantage of using the EP/IC resins, known to date, in processes analogous to injection molding, that the resulting molded materials have mechanical properties inferior to those produced in conventional casting and hardening of these reaction resins as indicated by the data presented in Table 2 below.
TABLE 2 __________________________________________________________________________ Influence of Standard-Rod Fabrication Conditions on the Molded Material Properties of Cross Linked EP/IC Resins (Formula mole ratio EP/IC &lt;1) Molding Material Properties EP/IC Resin Mole Ratio Standard Rod BF SZ T.sub.M Components.sup.(1) EP:IC Fabrication Conditions.sup.(2) N/mm.sup.2 Nmm/mm.sup.2 .degree.C. __________________________________________________________________________ BAGE;MDI 0.5 KGT: 1 h 130.degree. C. 105 6 235 QM I (66%) 3 h 130.degree. C., 16 h 200.degree. C. BCl.sub.3.DMBA(1.5%).sup.(3) 0.5 NSG (3 bar): 10 min 150.degree. C., 76 4 209 16 h 200.degree. C. NOEP, PPGE.sup.(4) ; MDI 0.37 KGT: 1 h 110.degree. C. 115 12 225 QM II (66%) 4 h 140.degree. C., 16 h 200.degree. C. BCl.sub.3.DMBA(1,5%).sup.(3) 0.37 NSG (2 bar): 8 min 140.degree. C., 96 8.3 216 16 h 200.degree. C. __________________________________________________________________________ .sup.(1) For chemical designation see Table 10 .sup.(2) KGT: Conventional casting technique, NSG: Lowpressure fastcastin technique .sup.(3) Catalyst concentration referred to resin matrix .sup.(4) Mole ratio NOEP:PPGE = 1.0
It is an object of the present invention to provide a low-viscosity reaction resin which can be filled to a high degree, that is easy to mix, hardens quickly and requires no solvents for use. Moreover, in comparison with acid anhydride-hardenable epoxy resins which have been used technically heretofore and were processed analogously to injection molding, the resins of this invention yield molded materials with substantially increased dimensional heat resistance and at the same time have good mechanical properties.